February 25, 2012

Pre-Neolithic Basque mtDNA gene pool (?)

I haven't read the paper, but I'm unconvinced that an 8,000 YBP estimate of separation (even if it were made with the precision of an atomic clock) "clearly supports" genetic continuity with the Paleolithic/Mesolithic settlers of the Franco-Cantabrian region.

Not only because the date in question is within a millennium or two of the arrival of the Neolithic in Iberia, one of those "curious coincidences."

Much more importantly, because the wisdom of Barbujani continues to be ignored when it comes to tying genetic age estimates to archaeology.

The American Journal of Human Genetics, 23 February 2012 doi:10.1016/j.ajhg.2012.01.002

The Basque Paradigm: Genetic Evidence of a Maternal Continuity in the Franco-Cantabrian Region since Pre-Neolithic Times

Doron M. Behar et al.

Different lines of evidence point to the resettlement of much of western and central Europe by populations from the Franco-Cantabrian region during the Late Glacial and Postglacial periods. In this context, the study of the genetic diversity of contemporary Basques, a population located at the epicenter of the Franco-Cantabrian region, is particularly useful because they speak a non-Indo-European language that is considered to be a linguistic isolate. In contrast with genome-wide analysis and Y chromosome data, where the problem of poor time estimates remains, a new timescale has been established for the human mtDNA and makes this genome the most informative marker for studying European prehistory. Here, we aim to increase knowledge of the origins of the Basque people and, more generally, of the role of the Franco-Cantabrian refuge in the postglacial repopulation of Europe. We thus characterize the maternal ancestry of 908 Basque and non-Basque individuals from the Basque Country and immediate adjacent regions and, by sequencing 420 complete mtDNA genomes, we focused on haplogroup H. We identified six mtDNA haplogroups, H1j1, H1t1, H2a5a1, H1av1, H3c2a, and H1e1a1, which are autochthonous to the Franco-Cantabrian region and, more specifically, to Basque-speaking populations. We detected signals of the expansion of these haplogroups at ∼4,000 years before present (YBP) and estimated their separation from the pan-European gene pool at ∼8,000 YBP, antedating the Indo-European arrival to the region. Our results clearly support the hypothesis of a partial genetic continuity of contemporary Basques with the preceding Paleolithic/Mesolithic settlers of their homeland.

6 comments:

"We detected signals of the expansion of these haplogroups at ∼4,000 years before present (YBP) and estimated their separation from the pan-European gene pool at ∼8,000 YBP, antedating the Indo-European arrival to the region."

Consistent with an expansion of these haplogroups out of the Pyrenean enclave at the end of the ice age ~8,000 years ago, leading to the pan European population.

Followed by a major expansion of the local female population after the neolithic arrived (~5,000 years ago)in Western Europe 4,000 years ago.

Nice evidence that the dominant mitochondrial haplogroup in Europe is pre-neolithic, and that it was the local female population that expanded after the neolithic arrived, at least in Spain.

But I wish I could see the calculations. Nothing I can see in the free stuff talks about non Basque European populations.

Occams Razor seems to apply rather than Barbujani. I suppose the Barbujani scenario is possible, but if so, from where did the Barbujani folk come from?

Is the "age of separation" even a reasonable metric to consider? They added 1 to the rho values for each of the specific suclades they analyzed. I would think the age of the subclade itself would be a more relevant metric. In any case, as you point out, Barbujani's critique seems to invalidate the conclusions of the paper. Behar et al. start by assuming that these haplogroups (H1, H3, H5) were in the Franco-Cantabrian region during the Paleolithic/Mesolethic, but there is still no compelling data to support that assumption.

"We detected signals of the expansion of these haplogroups at ∼4,000 years before present (YBP) and estimated their separation from the pan-European gene pool at ∼8,000 YBP, antedating the Indo-European arrival to the region. Our results clearly support the hypothesis of a partial genetic continuity of contemporary Basques with the preceding Paleolithic/Mesolithic settlers of their homeland."

The argument that there is meaningful matrilineal continuity between Epipaleolithic Iberia and Neolithic Iberia is quite a bit more tepid than the notion that both patrline and matriline ancestry in the Basque are predominantly (e.g. 80%+) from Upper Paleolithic/Mesolithic refugium populations. Matrilines tend to be more stable over time than patrilines. History offers many well documented examples of male dominated (or polygnyous incoming males in a gender balanced income population) incorporating local women into their culture with the children taking on the father's culture and language. If the oldest Basque private haplogroups broke off from the Pan-European gene pool ca. 8000 years old, the implication is that the oldest Basque NRY-DNA haplogroups shoud be no older and might very well be considerably younger. This implies a massive increase in Y-DNA haplogroup R1b frequency in Western Europe sometime in the Neolithic or later.

Also notable is that the mtDNA H haplogroups that are private to the Basque are not a good fit to pre-Last Glacial Maximum ancient DNA further North, although there are old mtDNA H ancient DNA samples in both North Africa (e.g. Natufian), and elsewhere in Southern Europe. One would expect lots of private mtDNA U4 and U5 haplogroups, not mtDNA H haplogroups, if that were the case.

Even then, I have to agree with Dienekes that a separation from the Pan-European gene pool ca. 8,000 years ago (i.e. 6,000 BCE) is very close in time to (i.e. within a thousand years of) the arrival of the Neolithic in Iberia, particularly given the error bars involved in the models that are used to derive those dates at that time depth (e.g. if one is a year and a half off in averge generation length, which is quite a bit less than 10% off, one is safely into the archaeologically documented Iberian Neolithic), and is too young by a factor of two or three for a lineage really showing continuity from the Franco-Cantabrian refugium which should show a break off ca. 16,000-24,000 BP, on the same order of magnitude as the founding mtDNA haplogroups of the Americas.

The scenario this data tends to favor in my mind is that these mtDNA haplogroups are part of a first wave Neolithic population, much of which is later replaced, but some of which introgresses into a later wave of population influx associated with the Basque culture which undergoes ethnogenesis sometime between 8000 BP and 4000 BP and then expands around 4000 BP until prevented from having further expansion by Indo-European advancement.

"Also notable is that the mtDNA H haplogroups that are private to the Basque are not a good fit to pre-Last Glacial Maximum ancient DNA further North, although there are old mtDNA H ancient DNA samples in both North Africa (e.g. Natufian), and elsewhere in Southern Europe. One would expect lots of private mtDNA U4 and U5 haplogroups, not mtDNA H haplogroups, if that were the case."

They found 20% U, but they did no further analysis of those results, not even to identify percentages of U subclades. I think they missed the boat, they might have learned something interesting by looking at diversity in the haplogroups that we know are very old instead of focusing exclusively on H which we know to be relatively young. It looks like their haplogroup percentages are similar to much of the rest of Europe.

Actually, there is a study which found 15.5% of U5b in Northern Navarrese (which are ethnically Basque, and speak Basques), that's one of the highest percentages found in Europe. (The study is Cardoso et al. 2011).

Thank you! I noticed this as well. I'm glad I'm not the only one noticing that if H1 is only 10,000 years old, and if Basque population markers are being brought into the picture as well, then both represent Neolithic migration.

They appear unaware there WAS Neolithic migration. They present the next migration after that of the Magdalenian people, as the Indo-Europeans.

Last I heard, the Basques pretty much genetically resemble the people of Cyprus or one of its island neighbors, and share language features with it as well. That was the route of migration of the Mediterranean branch of Neolithic expansion - along the Mediterranean coast to Spain.

I actually looked at the papers to try to determine where H1am would be from. I guess not from Basque, or they'd have said so? I hope they aren't basing all that rapid expanson out of Spain on five samples from Spain? I happen to be H1am1 on their new phylogenetic tree, so I definitely want the location where H1am was found. Genbank doesn't say (JQ703706), and I can't find where any papers give teh characteristics of their sample. Allegedly these samples were for the other 2012 paper.

If anyone knows how to get at that information. I tried writing to Behar and to Van Oven, and neither has responded so far.

Maybe tehy might want to share that information before more people plow through their papers in search of that data and realize that by their evidence, haplogroup H1 isn't no paleolithic phenomenon in Spain. If we don't have to plow through their work looking for obvious information, maybe not alot of people will realize that! They might want to move quickly to make full information on their data more available with less work. ;)

Thank you. I wanted my mtdna line ancestor to be from the East or the Middle East and Neolithic, not my only ancestor who spent theh last ice age in a teepee in Spain.

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